When secondary cpus are initialized during an i386 pv-guest restore
(due to save/restore or live migration), and the guest has
a load that generates a fair number of interrupts (e.g., parallel kernel make),
a stack overflow can occur because cpu_initialize_context() has
a 2800 byte structure it declares on its stack. linux-i386 has 4K stacks, by
default.
Using 2800 bytes out of 4K by a single function in a call list isn't nice;
add the beginning of interrupt handling at just the right point, before the
switch to the interrupt stack is made... and... the scale tips...
Simple fix: malloc & free structure as needed.
Would fail save/restore testing of an i386-guest running a parallel, kernel
make after
50->100 save/restores; with the fix, haven't seen it fail after 650
save/restores.
Note: this is a basic port of this function in Jeremy Fitzharinge's Xen
implementation of pv-ops
in upstream Linux, part of 15/32 patch, Xen SMP guest support.
Original patch done on rhel5; did a simple diff & merge to xen-unstable's
version
of smpboot.c to generate the attached patch, so it cleanly applies; but
haven't built/run/tested the xen-unstable version.
Signed-off-by: Donald Dutile <ddutile@xxxxxxxxxx>
--- linux-2.6.18-xen.hg/drivers/xen/core/smpboot.c.orig 2008-01-31
13:45:10.000000000 -0500
+++ linux-2.6.18-xen.hg/drivers/xen/core/smpboot.c 2008-01-31
13:56:07.000000000 -0500
@@ -180,9 +180,9 @@
cpu_idle();
}
-static void __cpuinit cpu_initialize_context(unsigned int cpu)
+static int cpu_initialize_context(unsigned int cpu)
{
- vcpu_guest_context_t ctxt;
+ vcpu_guest_context_t *ctxt;
struct task_struct *idle = idle_task(cpu);
#ifdef __x86_64__
struct desc_ptr *gdt_descr = &cpu_gdt_descr[cpu];
@@ -191,58 +191,65 @@
#endif
if (cpu_test_and_set(cpu, cpu_initialized_map))
- return;
+ return 0;
- memset(&ctxt, 0, sizeof(ctxt));
+ ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
+ if (ctxt == NULL)
+ return -ENOMEM;
- ctxt.flags = VGCF_IN_KERNEL;
- ctxt.user_regs.ds = __USER_DS;
- ctxt.user_regs.es = __USER_DS;
- ctxt.user_regs.fs = 0;
- ctxt.user_regs.gs = 0;
- ctxt.user_regs.ss = __KERNEL_DS;
- ctxt.user_regs.eip = (unsigned long)cpu_bringup_and_idle;
- ctxt.user_regs.eflags = X86_EFLAGS_IF | 0x1000; /* IOPL_RING1 */
+ memset(ctxt, 0, sizeof(*ctxt));
- memset(&ctxt.fpu_ctxt, 0, sizeof(ctxt.fpu_ctxt));
+ ctxt->flags = VGCF_IN_KERNEL;
+ ctxt->user_regs.ds = __USER_DS;
+ ctxt->user_regs.es = __USER_DS;
+ ctxt->user_regs.fs = 0;
+ ctxt->user_regs.gs = 0;
+ ctxt->user_regs.ss = __KERNEL_DS;
+ ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
+ ctxt->user_regs.eflags = X86_EFLAGS_IF | 0x1000; /* IOPL_RING1 */
- smp_trap_init(ctxt.trap_ctxt);
+ memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));
- ctxt.ldt_ents = 0;
+ smp_trap_init(ctxt->trap_ctxt);
- ctxt.gdt_frames[0] = virt_to_mfn(gdt_descr->address);
- ctxt.gdt_ents = gdt_descr->size / 8;
+ ctxt->ldt_ents = 0;
+
+ ctxt->gdt_frames[0] = virt_to_mfn(gdt_descr->address);
+ ctxt->gdt_ents = gdt_descr->size / 8;
#ifdef __i386__
- ctxt.user_regs.cs = __KERNEL_CS;
- ctxt.user_regs.esp = idle->thread.esp0 - sizeof(struct pt_regs);
+ ctxt->user_regs.cs = __KERNEL_CS;
+ ctxt->user_regs.esp = idle->thread.esp0 - sizeof(struct pt_regs);
- ctxt.kernel_ss = __KERNEL_DS;
- ctxt.kernel_sp = idle->thread.esp0;
+ ctxt->kernel_ss = __KERNEL_DS;
+ ctxt->kernel_sp = idle->thread.esp0;
- ctxt.event_callback_cs = __KERNEL_CS;
- ctxt.event_callback_eip = (unsigned long)hypervisor_callback;
- ctxt.failsafe_callback_cs = __KERNEL_CS;
- ctxt.failsafe_callback_eip = (unsigned long)failsafe_callback;
+ ctxt->event_callback_cs = __KERNEL_CS;
+ ctxt->event_callback_eip = (unsigned long)hypervisor_callback;
+ ctxt->failsafe_callback_cs = __KERNEL_CS;
+ ctxt->failsafe_callback_eip = (unsigned long)failsafe_callback;
- ctxt.ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
+ ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
#else /* __x86_64__ */
- ctxt.user_regs.cs = __KERNEL_CS;
- ctxt.user_regs.esp = idle->thread.rsp0 - sizeof(struct pt_regs);
+ ctxt->user_regs.cs = __KERNEL_CS;
+ ctxt->user_regs.esp = idle->thread.rsp0 - sizeof(struct pt_regs);
- ctxt.kernel_ss = __KERNEL_DS;
- ctxt.kernel_sp = idle->thread.rsp0;
+ ctxt->kernel_ss = __KERNEL_DS;
+ ctxt->kernel_sp = idle->thread.rsp0;
- ctxt.event_callback_eip = (unsigned long)hypervisor_callback;
- ctxt.failsafe_callback_eip = (unsigned long)failsafe_callback;
- ctxt.syscall_callback_eip = (unsigned long)system_call;
+ ctxt->event_callback_eip = (unsigned long)hypervisor_callback;
+ ctxt->failsafe_callback_eip = (unsigned long)failsafe_callback;
+ ctxt->syscall_callback_eip = (unsigned long)system_call;
- ctxt.ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(init_level4_pgt));
+ ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(init_level4_pgt));
- ctxt.gs_base_kernel = (unsigned long)(cpu_pda(cpu));
+ ctxt->gs_base_kernel = (unsigned long)(cpu_pda(cpu));
#endif
- BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, &ctxt));
+ BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, ctxt));
+
+ kfree(ctxt);
+ return 0;
}
void __init smp_prepare_cpus(unsigned int max_cpus)
@@ -400,7 +407,9 @@
if (rc)
return rc;
- cpu_initialize_context(cpu);
+ rc = cpu_initialize_context(cpu);
+ if (rc)
+ return rc;
if (num_online_cpus() == 1)
alternatives_smp_switch(1);
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